Cyclonic air filter assembly for an engine

ABSTRACT

An internal combustion engine includes an engine block, an air-fuel mixing device, and an air filter assembly. The air filter assembly includes a housing, a filter element, and a gap between the filter element and the housing. The housing includes a base and a cover which define an interior volume. The housing includes an outlet passage fluidly coupling a filtered air outlet to a final air outlet. The filter element divides the interior volume into a filtered volume and an unfiltered volume. The gap is configured to direct air in a first airflow pass before being filtered by the filter element. The filter element is configured to direct filtered air in a second airflow pass in a substantially opposite direction from the first airflow pass. The outlet passage is configured to direct filtered air into a third airflow pass in a substantially same direction as the first airflow pass.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/347,953, filed May 7, 2019, which claims priority to PCT ApplicationNo. PCT/US2017/061,147 filed Nov. 10, 2017, which claims the benefit ofand priority to U.S. Provisional Application No. 62/421,098, filed Nov.11, 2016, and U.S. Provisional Application No. 62/460,032, filed Feb.16, 2017, all of which are hereby incorporated by reference in theirentireties.

BACKGROUND

The present application generally relates to the field of air filtersand air filter assemblies, such as those for use with internalcombustion engines.

An internal combustion engine typically includes an air filter forremoving debris, including, dust, dirt, grass clippings, etc. from airentering the engine for combustion processes. The air filter assemblymay be housed in a case and include a filter element, which includesfilter media, such as filter paper, foam, mesh, or other media. Afterpassing through the filter media, the filtered air is routed to acarburetor or other air-fuel mixing device to be mixed with fuel andthen to a combustion chamber of the engine. Removing debris from the airhelps to preserve the moving components of the engine, such as thepiston and crankshaft, avoiding excess friction and wear, as well aspreventing clogging of the fuel delivery system.

SUMMARY

One embodiment of the invention includes an internal combustion engine.The internal combustion engine includes an engine block including acylinder and an air-fuel mixing device configured to provide an air-fuelmixture to the cylinder. The air filter assembly is configured toprovide filtered air to the air-fuel mixing device. The air filterassembly includes a housing, a filter element, and a gap between thefilter element and the housing. The housing includes a base and a cover.The base and the cover define an internal volume. The housing includesan air intake, a filtered air outlet, and an outlet passage fluidlycoupling the filtered air outlet to a final air outlet. The filterelement is positioned within the interior volume. The filter elementdivides the interior volume into a filtered volume and a unfilteredvolume. The gap is configured to direct filtered air in a first airflowpass before being filtered by the filter element. The filter element isconfigured to direct filtered air in a second airflow pass in asubstantially opposite direction from the first airflow pass. The outletpassage is configured to direct filtered air into a third airflow passin a substantially same direction as the first airflow pass.

In some embodiments, the cover is configured to releasably fasten to thebase. In some embodiments, the housing comprises a first housing endportion and a second housing end portion.

In some embodiments, the base includes the air intake, the filtered airoutlet, and the outlet passage.

In some embodiments, the first housing end portion includes the airintake and the filtered air outlet. In some embodiments, the secondhousing end portion includes a debris outlet configured to allow debrisand air to exit the housing.

In some embodiments, the gap is configured to direct air in the firstairflow pass in a direction from the first housing end portion towardthe second housing end portion.

In some embodiments, the housing includes a plurality of ribs formed inthe cover and the base to direct air from the air intake toward a debrisoutlet formed in the base.

In some embodiments, the air filter assembly includes a trough formed inthe base near the debris outlet, wherein the trough narrows from anentrance to an exit and is configured to direct debris toward the debrisoutlet.

In some embodiments, the plurality of ribs extend more than halfway intothe gap.

In some embodiments, the plurality of ribs in the cover comprise helicalribs and the plurality of ribs in the base comprise helical ribs.

In some embodiments, the plurality of ribs in the cover align with theplurality of ribs in the base to form a plurality of angled air channelswithin the housing.

In some embodiments, the first of the plurality of angled air channelsis narrower than a remainder of the plurality of angled air channels. Insome embodiments, the first of the plurality of angled air channels ispositioned proximate the air intake such that air enters the first ofthe plurality of angled air channels before entering the remainder ofthe plurality of angled air channels.

In some embodiments, the air intake comprises an L-shape having a firstportion and a second portion. In some embodiments, the first portion isconfigured to direct incoming air flow to substantially complete a firstfiltering pass within a first angled air channel before joining withincoming air flow from the second portion.

In some embodiments, the air filter assembly is oriented horizontallywith the engine in a normal operating position.

Another embodiment of the invention includes an air filter assemblyconfigured to provide filtered air to an engine. The air filter assemblyincludes a housing, a filter element, an air intake, a debris outlet, afiltered air outlet, a gap between the filter element and the housing,and a plurality of ribs. The housing includes a cover and a base. Thecover and the base define an interior volume of the housing. The filterelement is positioned within the volume and includes filter media. Thefilter element devices the interior volume into a filtered volume and anunfiltered volume. The air intake is formed in the base and isconfigured to allow air to flow into the housing. The debris outlet isformed in the base and is configured to allow debris and air to exit thehousing. The filtered air outlet is formed in the base. The filtered airoutlet is fluidly coupled to an air-fuel mixing device to allow filteredair to exit the housing and enter the air fuel-mixing device. The gap isconfigured to allow air to flow between the filter element and thehousing. The plurality of ribs is configured to direct air to completeat least two cyclonic filtering passes within the gap before beingfiltered by the filter element.

In some embodiments, the plurality of ribs extend more than halfway intothe gap.

In some embodiments, the plurality of ribs in the cover align with theplurality of ribs in the base to form a plurality of angled air channelswithin the housing.

In some embodiments, one of the plurality of angled air channels isnarrower than a remainder of the plurality of angled air channels. Insome embodiments, one of the plurality of angled air channels ispositioned proximate the air intake such that incoming air enters theone of the plurality of angled air channels before entering theremainder of the plurality of angled air channels.

In some embodiments, the air filter assembly includes a trough formed inthe base near the debris outlet.

In some embodiments, air flows into the housing from the air intakebased on intake pressure pulses created from reciprocation of a piston.

Another embodiment of the invention includes an internal combustionengine. The engine includes an engine block including a cylinder, anair-fuel mixing device configured to provide an air fuel mixture to thecylinder, and an air filter assembly configured to provide filtered airto the air-fuel mixing device. The air filter assembly includes ahousing, a filter element, an outlet passage, and an air intake. Thehousing includes a base and a cover. The cover is configured toreleasably fasten to the base. The housing defining a first housing endportion and a second housing end portion. The base and the cover definean interior volume. The filter element is positioned within the interiorvolume. The filter element divides the interior volume into a filteredvolume and an unfiltered volume. The outlet passage is formed in thebase and fluidly couples a filtered air outlet to a final air outlet.The filtered air outlet is in fluid communication with the filteredvolume of the filter element. The air intake is formed in the housing atthe first housing end portion and is configured to allow air to flowinto a gap between the filter element and the housing. The gap isconfigured to direct air within the gap in a first airflow pass in adirection from the first housing end portion toward the second housingend portion before being filtered by the filter element. The filterelement is configured to direct the filtered air in a second airflowpass in a substantially opposite direction from the first airflow pass.The outlet passage is configured to direct filtered air into a thirdairflow pass in a substantially same direction as the first airflowpass.

Another embodiment of the invention includes an internal combustionengine. The engine includes an engine block including a cylinder, anair-fuel mixing device configured to provide an air-fuel mixture to thecylinder, and an air filter assembly configured to provide filtered airto the air-fuel mixing device. The air filter assembly includes ahousing comprising a cover and a base, where the cover is configured toreleasably fasten to the base and the cover and the base define aninterior volume of the housing, and a filter element positioned withinthe interior volume comprising a first end portion, a second endportion, and filter media extending between the first end portion andthe second end portion. The filter element divides the interior volumeinto a filtered volume and an unfiltered volume. A gap is formed betweenthe filter element and the housing and is configured to allow air toflow between the filter element and the housing. An air intake is formedin the base and is configured to allow air to flow into the housing. Adebris outlet is formed in the base and is configured to allow debrisand air to exit the housing. A filtered air outlet is formed in the baseand in fluid communication with the filtered volume of the filterelement, where the filtered air outlet is fluidly coupled to theair-fuel mixing device to allow filtered air to exit the housing andenter the air-fuel mixing device. One or more ribs are formed in thecover and the base to direct an air flow from the air intake toward thedebris outlet. The ribs are configured to direct the air flow tocomplete at least two cyclonic filtering passes within the gap beforebeing filtered by the filter element. In some embodiments, the ribsextend more than halfway into the gap. In some embodiments, the ribs inthe cover align with the ribs in the base to form one or more angled airchannels within the housing. In some embodiments, first of the angledair channels is narrower than a remainder of the angled air channels. Insome embodiments, the first of the angled air channels is positionedproximate the air intake such that incoming air enters the first of theangled air channels before entering the remainder of the angled airchannels. In some embodiments, the air intake includes an L-shape havinga first portion and a second portion. The first portion is configured todirect incoming air flow to substantially complete a cyclonic filteringpass within a first angled air channel before joining with incoming airflow from the second portion. In some embodiments, a target exitvelocity of air exiting from the debris outlet is 30 feet per second. Insome embodiments, air flow within the housing is substantially laminarduring the at least two cyclonic filtering passes. In some embodiments,the filter media includes a debris-shedding filter media such thatdebris falls off the filter media due to engine vibrations at enginespeeds up to an engine idle speed. In some embodiments, the filter mediaincludes a debris-shedding filter media such that debris falls off thefilter media due to engine vibrations within a predetermined frequencyrange. In some embodiments, the air intake extends linearly between afirst surface and a second surface, where the second surface is aninterior surface of the base. In some embodiments, the debris outletincludes a valve configured to open and close in response to changes ina pressure of the interior volume of the housing. In some embodiments,the air filter assembly further includes a trough formed in the basenear the debris outlet, where the trough is configured to direct debristoward the debris outlet. In some embodiments, the air flows into thehousing from the air intake based on intake pressure pulses created fromreciprocation of a piston.

Another embodiment of the invention includes an air filter housingconfigured to use with an engine. The air filter housing includes a baseincluding a base mounting flange and an air outlet conduit, where thebase defines a first portion of an interior volume configured to receivea filter element, and where the base mounting flange includes a firstfastener opening and the air outlet conduit includes a second fasteneropening. The housing further includes a cover including a cover mountingflange, a third fastener opening, and a fourth fastener opening, wherethe cover defines a second portion of the interior volume, and where, inan attached configuration in which the base mounting flange is alignedwith and in contact with the cover mounting flange, the first fasteneropening is aligned with the third fastener opening and the secondfastener opening is aligned with the fourth fastener opening. A firstfastener is inserted into the first fastener opening and the thirdfastener opening and a second fastener inserted into the second fasteneropening and the fourth fastener opening. In some embodiments, the secondfastener opening is spaced apart from the base mounting flange. In someembodiments, an entrance to the first fastener opening is spaced apartfrom an entrance to the second fastener opening by a first distance. Insome embodiments, the first fastener opening is threaded and wherein thesecond fastener opening is threaded. In some embodiments, the air filterhousing further includes a first threaded insert positioned in the firstfastener opening and a second threaded insert positioned in the secondfastener opening. In some embodiments, the base mounting flange includesa channel configured to receive a gasket.

Another embodiment of the invention includes an air filter housingconfigured for use with an engine. The air filter housing includes abase defining a first portion of an interior volume configured toreceive a filter element, where the base includes an air filter outletin fluid communication with the interior volume and a final outletconfigured to provide fluid communication to an air-fuel mixing device,and where the base includes an outlet conduit fluidly coupling the airfilter outlet to the final outlet and at least a portion of the outletconduit is located below the interior volume. The housing furtherincludes a cover defining a second portion of the interior volume andconfigured to be removably attached to the base. In some embodiments,the base includes an elbow including a mounting flange configured toattach to the air-fuel mixing device, where the final outlet is formedin the mounting flange. In some embodiments, the elbow is an integralcomponent of the base. In some embodiments, the elbow is attached to thebase. In some embodiments, the elbow is ultrasonically welded to thebase.

Another embodiment of the invention includes an air filter elementconfigured for use with an air filter housing of an engine. The airfilter element includes a first end portion having a first body and aboss extending outward away from the first body, where the first endportion is formed from a first material having a first hardness, asecond end portion having a second body and defining an opening formedthrough the second body, where the second end portion is formed from asecond material having a second hardness less than the first hardness,and filter media positioned between the first end portion and the secondend portion. In some embodiments, an outer diameter of the boss is lessthan an outer diameter of the first body. In some embodiments, the outerdiameter of the boss is at most half of the outer diameter of the firstbody. In some embodiments, the first material includes urethane foam andthe second material comprises urethane foam. In some embodiments, theboss is centrally located on the first body.

Another embodiment of the invention includes an air filter assemblyconfigured to provide filtered air to an engine. The air filter assemblyincludes a housing defining an interior volume configured to receive afilter element, where the housing includes first housing end portionhaving an air filter conduit in fluid communication with the interiorvolume and a second housing end portion, where the air filter conduitdefines an air filter outlet and includes a crossbar positioned in theair filter outlet, a filter element including a first end portion havinga first body and a boss extending outwardly away from the first body, asecond end portion having a second body and an opening formed throughthe second body, and filter media positioned between the first endportion and the second end portion. In a first orientation of the filterelement, the first end portion of the filter element is positioned nearthe first housing end portion with the boss in contact with the firstend portion, and the second end portion of the filter element ispositioned near the second housing end portion with a portion of the airfilter conduit positioned within the opening. In a second orientation ofthe filter element, the first end portion of the filter element ispositioned near the second housing end portion with the boss in contactwith the crossbar of the air filter outlet, thereby preventinginstallation of the filter element within the interior volume. In someembodiments, the second housing end portion includes a wall locatedopposite the air filter conduit and in the first orientation of thefilter element, the boss contacts the wall. In some embodiments, thesecond housing end portion includes a wall located opposite the airfilter conduit and the wall includes a recess and in the firstorientation of the filter element, at least a portion of the boss ispositioned within the recess. In some embodiments, the first end portionis formed from a first material having a first hardness and the secondend portion is formed from a second material having a second hardnessless than the first hardness. In some embodiments, an outer diameter ofthe boss is less than an outer diameter of the first body. In someembodiments, the outer diameter of the boss is at most half of the outerdiameter of the first body. In some embodiments, the first materialincludes urethane foam and wherein the second material includes urethanefoam. In some embodiments, the boss is centrally located on the firstbody. In some embodiments, in the first orientation of the filterelement, the first end portion of the filter element exerts a force onthe air filter element directed toward the air filter conduit to form aseal between the second end portion of the filter element and the airfilter conduit. In some embodiments, an outer diameter of the boss isless than an outer diameter of the first body. In some embodiments, theouter diameter of the boss is at most half of the outer diameter of thefirst body.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, in which:

FIG. 1 is a perspective view of an internal combustion engine, accordingto an exemplary embodiment.

FIG. 2 is a rear perspective view of the internal combustion engine ofFIG. 1.

FIG. 3 is a perspective view of an air filter assembly, according to anexemplary embodiment.

FIG. 4 is a rear perspective view of the air filter assembly of FIG. 3.

FIG. 5 is a front perspective view of a filter element of the air filterassembly, according to an exemplary embodiment.

FIG. 5A is a front perspective view of a filter element of the airfilter assembly, according to an exemplary embodiment.

FIG. 5B is a rear perspective view of the filter element of FIG. 5.

FIG. 6 is a perspective view of the air filter assembly of FIG. 3 withthe cover removed.

FIG. 7 is a rear perspective view of the air filter assembly of FIG. 3with the cover removed.

FIG. 8 is a top perspective view of the air filter assembly of FIG. 3with the cover and filter removed.

FIG. 9 is a top view of a base of the air filter assembly of FIG. 3.

FIG. 10 is a bottom view of a cover of the air filter assembly of FIG.3.

FIG. 11 is a sectional view of the air filter assembly, taken along line11-11 of FIG. 3.

FIG. 12 is a sectional view of the base of the air filter assembly,taken along line 12-12 of FIG. 9.

FIG. 13 is a sectional view of the air filter assembly, taken along line13-13 of FIG. 4.

FIG. 14 is a sectional view of the air filter assembly, taken along line14-14 of FIG. 11.

FIG. 15 is a sectional view of the air filter assembly, taken along line15-15 of FIG. 4.

FIG. 16 is a perspective view of a base of an air filter assembly,according to an exemplary embodiment.

FIG. 17 is another perspective view of the base of FIG. 16.

FIG. 18 is another perspective view of the base of FIG. 16.

FIG. 19 is a section view of the base of FIG. 16 and an air filterelement.

FIG. 20 is a top view of the base of FIG. 16.

FIG. 21 is a perspective view of the base of FIG. 16.

FIG. 22 is a detail view of the base of FIG. 16.

FIG. 23 is a perspective view of a cover of an air filter assembly,according to an exemplary embodiment.

FIG. 24 is a detail view of the cover of FIG. 23.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the presentapplication is not limited to the details or methodology set forth inthe description or illustrated in the figures. It should also beunderstood that the terminology is for the purpose of description onlyand should not be regarded as limiting.

Referring to FIGS. 1-2, an engine shown as an internal combustion engine100 is illustrated according to an exemplary embodiment. The internalcombustion engine 100 includes an engine block 101 having one or morecylinders, cylinder heads, pistons, and a crankshaft 110. Each pistonreciprocates in a cylinder along a cylinder axis to drive the crankshaft110. The crankshaft 110 rotates about a crankshaft axis 112. Thecrankshaft 110 is positioned in part within a crankcase 114. In anexemplary embodiment, the crankshaft 110 may be oriented horizontally(i.e., a horizontal engine) with the engine 100 in its normal operatingposition. In other embodiments, the crankshaft 110 is verticallyoriented (i.e., a vertical engine) with the engine 100 in its normaloperating position. The engine may include one cylinder or two or morecylinders. The engine 100 also includes an air-fuel mixing device 128for supplying an air-fuel mixture to the cylinder (e.g., a carburetor,an electronic fuel injection system, a fuel direct injection system,etc.), an air filter assembly 102, and a muffler 120.

The engine 100 can be used on a variety of end products, includingoutdoor power equipment, portable jobsite equipment, and standby orportable generators. Outdoor power equipment includes lawn mowers,riding tractors, snow throwers, pressure washers, tillers, logsplitters, zero-turn radius mowers, walk-behind mowers, riding mowers,stand-on mowers, pavement surface preparation devices, industrialvehicles such as forklifts, utility vehicles, commercial turf equipmentsuch as blowers, vacuums, debris loaders, overseeders, power rakes,aerators, sod cutters, brush mowers, etc. Outdoor power equipment may,for example, use the engine 100 to drive an implement, such as a rotaryblade of a lawn mower, a pump of a pressure washer, an auger of a snowthrower, and/or a drivetrain of the outdoor power equipment. Portablejobsite equipment includes portable light towers, mobile industrialheaters, and portable light stands.

Referring to FIGS. 1-14, the engine 100 includes an air filter assembly102 according to an exemplary embodiment. The air filter assembly 102includes a filter element 160 positioned within a housing 132 formed bya cover 134 and a base 136. In an exemplary embodiment, the air filterassembly 102 is horizontally oriented such that the filter element 160is horizontally positioned within the housing 132 with the engine 100 inits normal operating position. In some embodiments, the crankshaft 110of the engine 100 is vertically oriented and the air filter assembly 102is horizontally oriented. The air filter assembly 102 is configured toprovide two stages of filtering of incoming air prior to supplying thefiltered air to the engine 100 for combustion processes. The firstfiltering stage includes cyclonic filtering of incoming air through theair filter assembly 102. The cyclonic filtering is configured to removelarge particles of debris prior to secondary filtering of the air. Thesecond filtering stage includes filtering of the partially filtered airthrough the filter element 160 to remove smaller particles of debrisfrom the incoming air. The filtered air is then sent to the air-fuelmixing device 128 of the engine 100 to be mixed with fuel prior tocombustion in the cylinder of the engine 100. The air filter assembly102 is positioned directly above the air-fuel mixing device 128 of theengine 100.

As shown in FIGS. 9-10, the interior surface 180 of the cover 134 andthe interior surface 182 of the base 136 combine to form an interiorvolume 155 (shown in FIG. 6) of the air filter assembly 102, with theinterior surface 180 of the cover 134 at least partially forming theinterior volume 155 and the interior surface 182 of the base 136 also atleast partially forming the interior volume 155. As shown in FIGS.13-14, the filter element 160 divides the interior volume 155 into anon-filtered volume 149 and a filtered volume 159. The non-filteredvolume 149 includes the space outside the filter element 160 and withinthe interior volume 155, and the filtered volume 159 includes the spaceinside the filter element 160. The cover 134 is designed to fasten andunfasten to the base 136 via aligned holes 170 (shown in FIGS. 9-10)formed in both the base 136 and cover 134. As shown in FIG. 12, thecover 134 includes fasteners 133 extending therethrough and configuredto fit within the holes 170 to fasten the cover 134 to the base 136. Thefasteners 133 are configured to rotate to lock and unlock the fastener133 in and out of engagement with the holes 170 in the base 136. Inother embodiments, other types of fasteners may be used (e.g., hinges,snaps, screws, etc.). Opening the cover 134 allows for insertion,removal, and checking of the status of the filter element 160 (shown inFIGS. 6-7) positioned within the interior volume 155 of the housing 132.In some embodiments, the cover 134 and base 136 are molded from aplastic material. In other embodiments, at least one of the cover 134and base 136 is stamped or assembled from aluminum, another material, oris formed from a combination of materials and manufacturing processes.

The air filter assembly 102 includes an air intake 138, a debris outlet142, and a filter outlet 168 formed in the base 136 of the air filterassembly 102. In other embodiments, the air intake 138, debris outlet142, and filter outlet 168 can be formed elsewhere in the housing 132(e.g., cover 134). As shown in FIGS. 8-9, the air intake 138 and debrisoutlet 142 are positioned on opposite sides and in opposite corners ofthe base 136. This relative positioning facilitates the cyclonic airfiltering processes described herein. Additionally, as shown in FIGS.8-9, the air intake 138 is positioned on the same side of the air filterassembly 102 as the filter outlet 168. This relative positioning helpsto position the air filter assembly 102 closely to the other componentsof the engine 100, including the air-fuel mixing device 128. The airintake 138 is positioned near the exterior of the engine 100 to draw inrelatively cool and clean air. If the air intake were positioned closerto the interior of the engine, the likelihood of drawing in relativelywarm and/or dirty air would increase. The positioning of components(e.g., fuel tank 116, muffler 120) due to the horizontally orientedcrankshaft 110 of the engine 100 is beneficial in combination with thehorizontally oriented air filter assembly 102 (along with the relativeplacement of the air intake 138 and filter outlet 168) to keep theoverall volume occupied by the engine 100 relatively compact. In otherembodiments, the engine 100 may be vertically-shafted, while the airfilter assembly 102 is horizontally oriented. As shown in FIG. 2, theair filter assembly 102 extends outward from the fuel tank 116 to adistance similar to the muffler 120. As shown in FIGS. 1-2, thecombination of the air filter assembly 102 and the muffler 120 has anoverall width similar to the width of the fuel tank 116. Positioning thefilter outlet 168 on the same side of the air filter assembly 102 as theair intake 138 allows the air filter assembly 102 to fit within theoverall footprint shared with the fuel tank 116 and the muffler 120 andbe positioned directly above the air-fuel mixing device 128. This helpsto keep the overall volume occupied by the engine 100 relativelycompact. If the filter outlet was positioned at the end of the airfilter assembly opposite the air intake, the resulting air filterassembly would likely extend outside of the footprint defined the fueltank and the muffler and increase the overall volume occupied by theengine.

As shown in FIG. 11, the air intake 138 is formed within the base 136 ofthe housing 132 and is configured to direct air into the unfilteredvolume 149 at an angle substantially tangential to a curved outersurface 163 of the filter element 160 to facilitate cyclonic filtering.In an exemplary embodiment, the air intake 138 extends from an outersurface of the base 136 to the interior surface 182 of the base 136 in alinear fashion such that the incoming air is not redirected uponentering the base 136. The air intake 138 has an L-shaped cross-section.The air intake 138 includes a first portion 135 and a second portion139. The first portion 135 is larger in cross-sectional area than thesecond portion 139. Air flowing through the first portion 135 maycomplete substantially one cyclonic pass around the filter 160 beforejoining with the air flowing through the second portion 139, therebyentraining at least some of the air in the second portion 139 andfacilitating the air flow through the second portion 139. Beneficially,this may increase the air flow velocity through the air intake 138. Insome embodiments, the air intake 138 has a rectangular shapedcross-section. In some embodiments, the air intake 138 has a circular,oblong, square, or otherwise shaped cross-section. In an exemplaryembodiment, the air intake 138 has a relatively small cross-sectionalarea so that a high incoming air flow velocity is maintained, whilestill allowing enough air to the engine 100 for combustion processes.

The debris outlet 142 includes a valve 143 (e.g., duckbill valve) thatallows debris removed from the cyclonic air flow to exit the air filterassembly 102 and additionally prevents backflow of the air and debrisinto the air filter assembly 102. The valve 143 opens and closes withchanges in the pressure of the interior volume 155. During periods ofrelatively low differential pressure (e.g., the difference in pressurebetween the interior volume 155 and the outside pressure) when a vacuummay exist within the interior volume 155, the valve 143 closes andduring periods of relatively high internal differential pressure, thevalve 143 opens. As such, changes in the internal pressure duringoperation of the engine 100 (e.g., due to intake pressure pulses at theair intake conduit 126 caused by reciprocation of the piston) opens andcloses the valve 143. Additionally, due to the pressure differences,incoming air is drawn into the air filter assembly 102 at a relativelyhigh velocity and is directed toward the debris outlet 142, where itslows due to a relatively open space 184 (e.g., and lower pressure)around the debris outlet 142. Larger debris is directed into or near thedebris outlet 142 due to the decreased velocity of the air at the debrisoutlet 142. A trough 186 (e.g., depressed pocket) is formed near thedebris outlet 142 in the interior surface 182 of the base 136. Thetrough 186 facilitates funneling or channeling debris toward the debrisoutlet 142. Additionally, as described below, a last rib 172 ispositioned next to the trough 186 and the debris outlet 142 to preventdebris blowback from the trough 186. For example, debris may accumulatein the trough 186 when the engine 100 is stopped and air stops flowingthrough the air filter assembly 102. When the engine 100 is restarted,air begins to flow through the air filter assembly 102 again and maydisturb and re-entrain debris collected in the trough 186. The placementof the last rib 172 next to the trough 186 helps to preventre-entrainment of collected debris so that the collected debris insteadexits the air filter assembly 102 through the debris outlet 142. Thetrough 186 is discussed further below with reference to FIG. 20.

As shown in FIGS. 9 and 15, the debris outlet 142 is positioned in thebase 136 in an opposite corner from the air intake 138. Air moving fromthe air intake 138 is cyclonically filtered around the filter element160 and is directed toward the space 184 located near the end 162 of thefilter element 160 where the air flow slows, allowing the debris to exitthe air flow and be drawn downward by gravity toward the debris outlet142. As such, debris in the incoming air is directed toward the debrisoutlet 142 instead of accumulating elsewhere within the base 136.Without the debris outlet 142 positioned near the space 184 near the end162 of the filter element 160, debris may remain suspended in the airflow. An opening 125 (FIGS. 8-9) in the ribs 152 in the base 136 allowsany debris that may remain within the base 136 to move through thehousing 132 toward the debris outlet 142. Further, the debris outlet 142is angled away (e.g., at approximately a 45 degree interior angle from avertical plane that includes the longitudinal axis 145 of the filterelement 160 when installed in the base 136) from the housing 132. Thedebris outlet 142 is positioned to direct debris exiting the air filterassembly 102 away from a spark plug of the engine 100 such that debrisdoes not accumulate on the spark plug.

The filter outlet 168 is formed within the base 136 of the housing 132and is configured to direct filtered air into an intake conduit 126 ofthe engine 100. The filter outlet 168 is positioned within and in fluidcommunication with the filtered volume 159 of the filter element 160.The filter outlet 168 is circular in cross-section. In otherembodiments, the filter outlet 168 can be oblong, square, rectangular,or otherwise shaped in cross-section. As shown in FIGS. 7 and 13, anoutlet conduit 156 (e.g., passage) includes a first passage 153 that isformed in the base 136 of the housing and a second passage 147 formed ina neck or elbow 158 that includes the mounting flange 177 for securingthe housing 132 to the air-fuel mixing device 128 of the engine 100(e.g., via bolts or other fasteners inserted through the bolt holes 154of the mounting flange 177). The first passage 153 of the outlet conduit156 is located below the interior volume 155. This arrangement helps toprovide a relatively compact air filter assembly 102 that can provideboth a cyclonic filtering stage and a filter media filtering stage androute the air filtered by both filtering stages to the air-fuel mixingdevice 128 by allowing the air filter stages and the routing of thefilter air in the first passage to occur within the same overallfootprint but at different elevations within the air filter assembly102.

In some embodiments, the base 136 and the elbow 158 are formed asseparate components and fastened together (e.g., by ultrasonic welding).In other embodiments, the base 136 and the elbow 158 are integrallyformed as a single piece (e.g., a single plastic molded part). Theoutlet conduit 156 extends between the filter outlet 168 and a finaloutlet 171 formed on the mounting flange 177 of the elbow 158. The finaloutlet 171 is formed within the mounting flange 177 of the elbow 158 andis in fluid communication with the outlet conduit 156 and the intakeconduit 126 of the engine 100. The final outlet 171 is circular incross-section. In other embodiments, the final outlet 171 can be oblong,square, rectangular, or otherwise shaped in cross-section. The outletconduit 156 is fluidly coupled by way of the intake conduit 126 to theair-fuel mixing device 128. The intake conduit 126 is directly coupledto the air-fuel mixing device 128. The intake conduit 126 may beseparate or may be at least partially integrated with the engine blockor cylinder head, and may be formed from metal, plastic, or othermaterials. The air filter assembly 102 is positioned directly above theair-fuel mixing device 128 of the engine 100 to allow the intake conduit126 to be directly coupled to the air-fuel mixing device 128 and toeliminate any need for an intermediate conduit or hose connecting theair filter assembly 102 to the air-fuel mixing device 128.

A gap 157 is formed between the interior surfaces 180, 182 of the cover134 and base 136, respectively, and the curved outer surface 163 of thefilter element 160. As shown by airflow path 192 in FIG. 13, the gap 157is configured to facilitate cyclonic filtering by directing the incomingair flow around the filter element 160 within the interior volume 155 ofthe housing 132. The gap 157 includes a gap distance 187 between theinterior surfaces 180, 182 and the curved outer surface 163 of thefilter element. The gap distance 187 is sized such that an incoming airflow velocity is maintained, without impeding air flow due to theproximity of the filter element 160 relative to the interior surfaces180, 182 of the cover 134 and base 136.

Referring now to FIGS. 12-14, the cover 134 and base 136 each includeribs 150, 152 (e.g., angled protrusions) extending axially inward fromthe interior surfaces 180, 182 of the cover 134 and base 136,respectively. The ribs 150, 152 are configured to facilitate a cyclonicfiltering effect within the housing 132 of the air filter assembly 102.As such, the ribs 150, 152 direct incoming air to follow the contour ofthe gap 157 between the curved outer surface 163 of the filter element160 and the interior surfaces 180, 182 of the cover 134 and base 136,respectively. In an exemplary embodiment, a last rib 172 is positionednear the trough 186 and the debris outlet 142 to prevent debris blowbackfrom the trough 186 and the debris outlet 142. The ribs 150, 152 extendin toward a longitudinal center axis 195 of the air filter assembly 102by a distance 189. The longitudinal center axis 195 is located in thecenter of the interior volume 155. In some embodiments, the longitudinalcenter axis 195 is included in a horizontal plane that defines a partingline between the cover 134 and the base 136 (e.g., the interface betweenthe mounting flanges 225 and 230 of the base 136 and the cover 134). Thedistance 189 is more than half of the gap distance 187 between theinterior surfaces 180, 182 and the outermost surface 163 of the filtermedia 161. The filter media 161 may be pleated paper such that theoutermost surface 163 is formed by a series of pleats or folds. Theoutermost surface 163 of the pleated paper filter media 161 defines agenerally circular cross-sectional shape. The ribs 150, 152 are of thesame height around the circumference of the interior surfaces 180, 182of the housing 132. In an exemplary embodiment, the ribs 150 in thecover 134 align with the ribs 152 in the base 136 to form one or moreangled air channels 151 within the housing 132. The alignment of theribs 150, 152 aids in directing the air flow to create the cyclonicfiltering effect (e.g., helical flow) within the housing 132. In someembodiments, the ribs 150, 152 are helical (i.e., helical ribs) to helpinduce the cyclonic filtering effect. The dimensions of the ribs 150,152 are formed so as to facilitate desired air flow through the angledair channels 151 for the filtering process. The rib height (e.g.,distance 189) being greater than half of the gap distance 187 helps tomaintain relatively high air flow velocity throughout the cyclonicfiltering stage. Maintaining the relatively high air flow velocity aidsin discharging debris near the debris outlet 142. In some embodiments,the ribs 150, 152 extend to a rib height (distance 189) that brings theribs 150, 152 into contact with the outermost surface 163 of the filtermedia 161, thereby forming closed channels in which the cyclonic airflow travels until the final channel which deposits debris toward thetrough 186. Applicant believes that relatively short rib heights (e.g.,25% or less of the gap distance 187) allows too much of the air flow toshort circuit across the cyclonic channels formed by the ribs 150, 152and reduces the efficiency on the cyclonic filtering operation. As shownin FIG. 13, a first air channel 174 is narrower in width than the otherair channels 151. The narrow width of the first air channel 174restricts the air flow through the first air channel 174 and increasesthe air flow velocity of the air flowing in from the air inlet 138.Ensuring a relatively high air flow velocity at the start of thecyclonic filtering process near the end 164 of the air filter element160 helps to maintain a relatively high air flow velocity throughout thecyclonic filtering process.

As shown in FIGS. 8-10, the ribs 150, 152 are axially arranged such thatthe desired air flow exit velocity is maintained (e.g., 30 feet persecond debris outlet target velocity). Referring to FIG. 8, the ribs150, 152 are arranged at an angle 181 relative to the interior surfaces180, 182 of the cover 134 and base 136, respectively, and at an angle183 relative to horizontal plane 173. As shown in FIG. 10, the ribs 150,152 are further arranged at an angle 185 relative to vertical plane 175.The arrangement of the ribs 150, 152 at angles 181, 183, 185 allow for atarget air flow exit velocity to be maintained, with minimal drag on theincoming air. In some arrangements, the placement, angle, and dimensionsof the ribs 150, 152 are configured using a screw-pitch typemeasurement, such as designating a set number of ribs over a length ofthe air filter assembly 102.

Referring to FIGS. 5-7, the filter element 160 is positioned within theinterior volume 155 (e.g., coupled to the base 136). The filter element160 includes an open or unsealed end or end portion 164 (FIG. 5B) and aclosed or sealed end or end portion 162 (FIG. 5) with filter media 161extending between the ends 162, 164. According to an exemplaryembodiment, the filter media 161 and ends 162, 164 combine to define afiltered volume, with the filter media 161 defining at least a portionof the filtered volume and the ends 162, 164 defining at least a portionof the filtered volume. In some such embodiments, the filter media 161is structured such that the filter media 161 has a closed-loop, such asthe periphery of a circle, ellipse, rectangle, or other closed-loopshape.

Referring to FIGS. 5-5B, the filter media 161 may be formed fromdifferent materials suitable for filtering debris from the intake airprovided for combustion by the engine 100 by being permeable to air butlargely preventing the ingress of dust and other contaminants from theunfiltered side to the filtered side. In some embodiments, the filtermedia 161 is pleated filter paper. In some embodiments, the filter media161 is a cellulose filter media. In other embodiments, and as describedfurther herein, the filter media 161 includes a debris-shedding filtermaterial. In some embodiments, such debris-shedding media is a nanomediaand includes multiple layers of cellulose media. In an exemplaryembodiment, the filter element 160 is substantially cylindrical in shapeso as to facilitate the cyclonic filtering of incoming air prior tofiltering by the filter media 161 by providing a curved outer surface163 for the air to flow around during cyclonic filtering (i.e., thefilter element 160 is symmetrical about a longitudinal center axis 145).In embodiments including a pleated filter media 161, the outermostsurface 163 of the pleated filter media 161 defines a generally circularcross-sectional shape and is considered to create a cylinder shapedfilter element 160.

In some embodiments, the ends 162, 164 are formed from a rigid material,such as plastic, cardboard, composite, aluminum, or other materials. Insome embodiments, the end 162 is formed from a harder material than theend 164 (i.e., the end 162 has a greater durometer than the end 164).For example, the end 162 may be formed from a hard urethane foam havinga relatively high durometer (e.g., a Type 3 urethane foam) and the end164 may be formed from a soft urethane foam have a relatively lowdurometer (e.g., a Type 2 urethane foam). The end 162 formed from theharder material includes a standoff, projection, or boss 121 thatextends outward from a main portion or body 122 of the end 162 (i.e.,away from the filter media 161). The boss 121 is centrally located onthe body 122 (i.e., the outer diameter 123 of the boss 121 and the outerdiameter 124 of the body 122 are both centered at the longitudinalcenter axis 145 of the filter element 160). The outer diameter 123 ofthe boss 121 is less than the outer diameter 124 of the body 122. Theend 164 formed from the softer material includes an opening 197 formedthrough the body 198 of the end 164 that allows filtered air from withinthe filter media 161 to exit the filter element 160. The softer materialhelps to form a seal between the end 164 and the conduit or duct (e.g.,filtered air passageway) to which the filter element 160 is attached.

In some embodiments, the filter media 161 is made from a debris-sheddingmedia. In such a case, the filter media 161 is configured to shed debrisdue to vibration. The debris-shedding media is constructed so thatvibrations within a particular or predetermined frequency range causedebris to fall off of the filter material. In some embodiments, duringwarm-up of an engine from a stopped condition to idle speeds of theengine 100 (e.g., 3600 revolutions per minute (RPM)), the engine 100vibrates in the frequency range of 10 Hz to 30 Hz. This vibration of theengine causes debris to fall off of the filter media 161. The debrisshed from the filter media 161 can be carried by the cyclonic air flowthrough the housing 132 and directed out of the valve 143 of the debrisoutlet 142.

As shown in FIG. 5A, in some embodiments, the filter element 160includes a guard or shield 148 that protects the filter media 161 fromimpacts. As shown in FIG. 5A, the guard 148 is an expanded metal cagethat surrounds the filter media 161. When the filter element 160 becomesclogged with debris, a user may remove the filter element 160 and shakeit to remove the accumulated debris. In certain instances, the user maystrike a solid object with the filter element 160 to help knock theaccumulated debris off of the filter media 161. The guard 148 protectsthe filter media 161 from damage that could otherwise be caused by suchan impact.

As shown in FIGS. 13-14, the opening 197 has the same size and shape asa protrusion or boss 169 of an air filter conduit or duct 156 thatsurrounds the filter outlet 168. The opening 197 receives the boss 169surrounding the filter outlet 168 to support the filter element 160 onthe boss 169 and create a seal 178 between the end 164 and the boss 169to prevent filtered air from reentering the interior volume 155 fromwithin the filter element 160. As shown in FIG. 13, the seal 178 extendslongitudinally for a distance of contact between the end 164 of thefilter element 160 and the boss 169 and, as shown in FIG. 11,circumferentially around the area of contact between the end 164 of thefilter element 160 and the boss 169. The filter element 160 mayadditionally be supported within the base 136 by a protrusion 137. Theprotrusion 137 may support the weight of the filter element 160 at anouter surface 163 of the end 162. The protrusion 137 may be an annularring shape so as to be of a similar shape as the outer surface 163 ofthe filter element 160. In some embodiments, as shown in FIGS. 20-21,the protrusion 137 is an air foil shape so as to both support the filterelement 160 and direct the cyclonic air flow toward the space 184 anddebris outlet 142. In other embodiments, the filter element 160 is onlysupported by the engagement between the end 164 and the boss 169surrounding the filter outlet 168. In an exemplary embodiment, the end162 is positioned proximate the debris outlet 142 and the end 164 ispositioned proximate the air inlet 138. As shown in FIGS. 13-14, thefilter element 160 is horizontally positioned within the housing 132 toalign the longitudinal center axis 145 of the filter element 160 withthe longitudinal center axis 195 of the base 136 of the air filterassembly 102. The boss 169 surrounding the filter outlet 168 issimilarly horizontally oriented with boss 169 extending horizontallyoutward from the surface 166 along the center axis 195. When the filterelement 160 is removed from the housing 132, the boss 169 shields thefilter outlet 168 from a direct path for any debris falling off of thefilter element 160. In some embodiments, the boss 169 has a length of0.5 inches or more. The horizontal arrangement of the filter element 160and the boss 169 means debris from the filter element 160 is less likelyto fall off and enter the filter outlet 168 as compared to a verticallypositioned filter and boss, in which any debris falling off of thefilter element would have a clear path to the outlet.

In operation, outside air flows into the air intake 138 of the airfilter assembly 102. The air intake 138 is positioned such that incomingair enters the housing 132 tangentially to the filter element 160 andnaturally flows into the cyclonic airflow path 192 established withinthe gap 157. The incoming air is not redirected during passage throughthe air intake 138. In an exemplary embodiment, the incoming air is notforced into the housing 132 using a fan, and instead air is drawn intothe housing 132 using pressure pulses created from the reciprocation ofthe piston during operation of the engine 100. Outside air moves pastthe air intake 138 and whatever air enters the air intake 138 naturallyflows from the air intake 138 into the unfiltered volume 149 of thehousing 132 and toward the debris outlet 142.

Once inside the housing 132, the incoming air is cyclonically filteredprior to being filtered by the filter element 160. The air flows aroundthe filter element 160 in the gap 157 formed between the outer surface163 of the filter element 160 and the interior surfaces 180, 182 of thecover 134 and base 136. During cyclonic filtration, large particles arefiltered from the incoming air and directed toward the debris outlet142. The incoming air completes at least two turns or cyclonic passesaround the filter element 160 within the gap 157 prior to being filteredby the filter element 160. Partially filtered air then flows through thefilter media 161 of the filter element 160 where smaller particles ofdebris are filtered out of the air. The filtered air flows into thefilter outlet 168, through outlet conduit 156, through the final outlet171 and into the intake conduit 126 of the engine 100. As shown in FIGS.13-14, the filter outlet 168 is in fluid communication with the filteredvolume 159 and is sealed against the end 164 of the filter element 160such that only filtered air is directed to the engine 100.

Referring to FIG. 13, the air filter assembly 102 includes a first endportion 165 and a second end portion 167. End 164 of the filter element160 is positioned proximate the first end portion 165 and end 162 of thefilter element 160 is positioned proximate the second end 167 such thatthe filter element 160 is horizontally oriented about center axis 195.As noted above, the air intake 138 is positioned on the same side (e.g.,first end 165) of the air filter assembly 102 as the filter outlet 168.The positioning of the air intake 138 relative to the filter outlet 168results in three passes of the air flow within the air filter assembly102 prior to entering the air-fuel mixing device 128.

The incoming air flows into the air intake 138 positioned on the firstend 165 and into the cyclonic airflow path 192 established within thegap 157 toward the second end 167 as designated by first airflow pass105. Accordingly, when completing the first airflow pass 105 (e.g.,completing at least one cyclonic air flow turn or pass around the filterelement 160), the incoming air moves from the air intake 138 toward thedebris outlet 142 positioned proximate the second end portion 167. Theoverall flow of air in the first airflow pass 105 is in a firstdirection from the first 165 toward the second end 167. The flow of airin the first airflow pass 105 moves cyclonically around the filterelement 160 but in a horizontal overall direction generally from end 165toward end 167 Next, the air flows through the filter media 161 of thefilter element 160 and toward the filter outlet 168 positioned proximatethe first end 165 as designated by second airflow pass 107. As such, thesecond airflow pass 107 is substantially parallel but opposite indirection to the first airflow pass 105. The flow of air in the secondairflow pass 107 moves in a horizontal overall direction generally fromend 167 toward end 165, which is opposite in direction to the first airflow pass 105. Finally, the air flows into the filter outlet 168 andturns back toward the second end 167 as designated by third airflow pass109 prior to entering elbow 158 that connects to the air-fuel mixingdevice 128. The outlet conduit 156 is configured to direct air in thethird airflow pass 109 toward the final outlet 171 in a substantiallyparallel direction to the first airflow pass 105 and second airflow pass107. Additionally, the third airflow pass 109 is in substantially thesame direction as the first airflow pass 105, but opposite in directionas the second airflow pass 107. The flow of air in the third air flowpass 109 moves in a horizontal overall direction generally from end 165toward end 167, which is the same direction as the first air flow pass105 and opposite the second air flow pass 107. The three air flow passes105, 107, and 109 are arranged in counter flow arrangements to theadjacent air flow pass or passes so that the air moving through thethree air flow passes travels in a first direction in the first air flowpass 105, is redirected in a second opposite direction in the second airflow pass 107, and returns to the first direction in the third air flowpass 109. Arranging the three air flow passes 105, 107, and 109 helps toprovide a relatively compact air filter assembly 102 that can provideboth a cyclonic filtering stage and a filter media filtering stage androute the air filtered by both filtering stages to the air-fuel mixingdevice 128. Air flow passes are considered to be substantially the samedirection when one air flow pass falls within plus or minus 25 degreesof the bearing of the referenced air flow pass in the same direction oftravel. Air flow passes are considered to be substantially the oppositedirection when one air flow pass falls within plus or minus 25 degreesof the bearing of the referenced air flow pass in the opposite directionof travel.

The ribs 150,152 create a cyclonic filtering effect within the housing132 of the air filter assembly 102. As mentioned above, the position,dimension, and angle of the ribs 150, 152 are configured to maintain atarget exit velocity (e.g., 30 ft/s) at the debris outlet 142.Additionally, the position, dimension, and angle of the ribs 150, 152may be selected such that incoming air completes at least two cyclonicpasses in the gap 157 prior to entering the filter element 160. Thecombination of the target exit velocity and at least two cyclonicfiltering passes increases the amount of debris removed from the airduring the cyclonic filtering stage.

The boss 121 of the filter element 160 has an outer diameter 123 that issmall relative to the outer diameter 124 of the body 122 of the end 162of the filter element 160 so that the boss 121 does not interfere withthe cyclonic air flow near the end 162 of the filter element 160. In oneembodiment, the outer diameter 123 of the boss 121 is no larger thanhalf the outer dimeter 124 of the body 122 to avoid interfering with thecyclonic air flow near the end 162 of the filter element 160.

Using the dimensions of the air intake 138, housing 132, ribs 150, 152,gap 157, and other components described herein, the velocity of the airflow within the housing 132 during cyclonic filtering is maintained atappropriate values so as to reduce any possible turbulent air flow andmaintain laminar flow of the incoming air. Maintaining laminar flowwithin the housing 132 during cyclonic filtration is desirable formaximum possible cyclonic filtering. The target velocity of the air atthe debris outlet 142 is approximately 30 feet per second (ft/s) tomaintain laminar flow for desirable cyclonic filtering. In otherarrangements, the target velocity of the air at the debris outlet 142can be more or less than 30 ft/s.

Cyclonic filtering of intake air prior to filtering by a filter elementas described above can facilitate longer engine runtime with a singlefilter. Because a large portion of debris is filtered prior to the airentering the filter, less debris is accumulated on the filter media.Thus, a filter assembly with cyclonic filtering will allow longer engineruntimes with a single filter. During filter testing conducted byApplicant, the air filter assembly 102 enabled the test engine to runlonger (5 hours versus almost 2 hours) before being starved for air tothe combustion process and collect less debris on the filter element (5grams versus 2 grams), indicating improved cyclonic filtering, whencompared to a conventional air filter assembly.

An alternative embodiment of the base 136 is illustrated in FIGS. 16-21.As shown in FIGS. 17-19, the air filter conduit 156 includes a crossbar200 (bar, wall, projection) positioned in the filter outlet 168. Asillustrated the crossbar 200 is set back from the edge of the boss 169of the air filter conduit 156. In other embodiments, the crossbar 200extends to the edge of the boss 169. As illustrated, the crossbar 200 ispositioned vertically within the filter outlet 168 and positioned in thecenter of the filter outlet 168. In other embodiments, the crossbar 200is positioned horizontally within the filter outlet 168 or at otherangles within the filter outlet 168. In some embodiments, the crossbar200 is one of multiple crossbars arranged in a grid or mesh within thefilter outlet 168. As shown in FIG. 19, the crossbar 200 functions tolimit insertion of the boss 121 of the filter element 160 into the airfilter conduit 156. When the filter element 160 is properly installed inthe interior volume 155 of the housing 132, the end 162 of the filterelement 160 including the boss 121 is positioned away from the airfilter conduit 156. The inclusion of the crossbar 200 within the airfilter conduit 156 prevents improper installation of the filter element160 with the end 162 positioned near the air filter conduit 156 bylimiting insertion of the boss 121 into the air filter conduit 156. Asshown in FIG. 19, when a user attempts to improperly install the filterelement 160 in this manner, the boss 121 contacts the crossbar 200 andthe opposite end 164 of the filter element 160 cannot be positionedwithin the interior volume 155. This arrangement error proofs assemblyof the filter element 160 into the housing 132 so that the filterelement 160 can only be positioned within the interior volume 155 whenoriented in a first orientation with the first end 162 of the filterelement 160 positioned near a first housing end portion 205 with theboss 121 in contact with the first housing end portion 205, and thesecond end 164 of the filter element 160 positioned near a secondhousing end portion 210 with the boss 169 or other portion of the airfilter conduit 156 positioned within the opening 197 of the second end164. In a second orientation of the filter element 160, the first end162 of the filter element 160 is positioned near the second housing endportion 210 with the boss 121 in contact with the crossbar 200 of thefilter outlet 168, thereby preventing installation of the filter element160 within the interior volume 155, as shown in FIG. 19.

As shown in FIG. 20, the first housing end portion 205 includes a wall215 that is in contact with the boss 121 when the filter element 160 isproperly installed within the interior volume 155. In some embodiments,a recess 220 (shown in broken lines) is formed in the wall 215 and atleast a portion of the boss 121 is positioned within the recess 220 whenthe filter element 160 is properly installed in the interior volume 155.As shown in FIG. 13, when the filter element 160 is properly installedwithin the interior volume 155 with the boss 121 contacting the firsthousing end portion 205, the first end 162 of the filter element 160exerts a force on the air filter element 160 directed toward the secondhousing end portion 210 and the air filter conduit 156 to form the seal178 between the second end 164 of the filter element 160 and the airfilter conduit 156. The relatively hard first end 162 of the filterelement 160 does not compress or deflect when the boss 121 contacts thefirst housing end portion 205 and forces the relatively soft second end164 of the filter element 160 onto the air filter conduit 156. Therelatively soft material of the second end 164 is chosen to help form anair tight seal 178 between the second end 164 and the air filter conduit156.

As shown in FIGS. 18-21, the base 136 includes a mounting flange 225that is arranged to align with and contact a corresponding mountingflange 230 of the cover 134 (as shown in FIG. 6) when the cover 134 isattached to the base 136. The mounting flange 225 is arranged in ahorizontal plane that includes the longitudinal center axis 195 of thehousing 132. The mounting flange 225 includes a recessed channel 235that receives a gasket (not shown) to form a seal between the mountingflanges 225 and 230 of the base 136 and the cover 134. The channel 235is formed between an outer wall 240 and an inner wall 245. Near the airintake 138, the inner wall 245 stops and the channel 235 is open to theair intake 138. One or more stakes or projections 250 are provided tohelp keep the gasket within the channel 235 near the air intake 138. Thestakes 250 extend above the channel 235 so that the gasket is positionedbetween the stakes 250 and the outer wall 240. If the base 136 and thecover 134 are not properly sealed by the gasket, the lack of a seal mayresult in pressure loss in the interior volume 155 which couldnegatively impact the velocity of the cyclonic air flow. The gaskethelps to prevent any moisture (e.g., rain) from entering the interiorvolume, which could negatively impact the function of the filter media161 if the filter media 161 got wet.

As shown in FIGS. 19-21, the portion of the mounting flange 225 near thefirst housing end portion 205 includes a first fastener opening 170A. Insome embodiments, as illustrated, the first fastener opening 170Aincludes a threaded insert 252 for coupling with a threaded fastener. Asecond fastener opening 170B is formed in an elbow 255 or otherstructure of the air filter conduit 156. In some embodiments, asillustrated, the second fastener opening 170B includes a threaded insert254 for coupling with a threaded fastener. The elbow 255 extends abovethe mounting flange 225 and provides the structure for forming a portionof the air filter conduit 156. As shown in FIG. 19, the entrance to thefirst fastener opening 170A is spaced apart from the entrance to thesecond fastener opening 170B by a distance 260. In the normal operatingposition of the air filter assembly 102, the entrance to the secondfastener opening 170B is located at a vertical elevation above thevertical elevation of the entrance to the first fastener opening 170A.Using the structure of the elbow 255 as a location for the secondfastener opening 170B helps to reduce the material needed to form thebase 136 by making dual use of the elbow 255 as both the structure of aportion of the air filter conduit 156 and the structure for receiving afastener for attaching the cover 134 to the base 136. This arrangementalso helps to keep the housing 132 relatively compact by allowing theportion of the mounting flange 225 near the second housing end portion210 to be narrower than the portion of the mounting flange 225 near thefirst housing end portion 205 by not having to accommodate the space andmaterial needed for the second fastener opening 170 in the mountingflange 225. As shown in FIG. 13, with the cover 134 and the base 136 inin an attached configuration in which the base mounting flange 225 isaligned with and in contact with the cover mounting flange 230, a thirdfastener opening 170C in the cover 134 is aligned with the firstfastener opening 170A and a fourth fastener opening 170D in the cover134 is aligned with the second fastener opening 170B. A first fastener133A is inserted into the third fastener opening 170C and the firstfastener opening 170A and attached to the base 136 (e.g., threads of thefastener 133A engage threads of the first fastener opening 170A or thethreaded insert 252). A second fastener 133B is inserted into the fourthfastener opening 170D and the second fastener opening 170B and attachedto the base 136 (e.g., threads of the fastener 133B engage threads ofthe second fastener opening 170B or the threaded insert 254).

FIGS. 20-21 also illustrate the trough 186 that leads to the debrisoutlet 142. The trough 186 includes a relatively wide entrance 262 thatnarrows to a relatively narrower exit 265. The relatively wide entrance262 helps to gather debris and direct debris toward the exit 265 of thetrough 186. The trough 186 is also pitched or angled between theentrance 262 to the exit 265 to direct debris from the entrance 262toward the exit 265. This arrangement helps to funnel debris filteredfrom the air flow by the cyclonic filtering process from the entrance262 toward the exit 265.

An alternative embodiment of the cover 134 is illustrated in FIGS. 23and 24. The cover 134 includes a first housing end 127 and a secondhousing end 129. The cover 134 includes two ribs 141 positioned at thefirst housing end 127. The ribs 141 protrude from an interior wall 193formed within the first housing end 127. The first housing end 127 isconfigured to receive the boss 121 on the first end 162 of the filterelement 160. As shown in FIG. 24, when assembled properly, the boss 121of the filter element 160 fits between the ribs 141 and seals againstwall 193. The ribs 141 limit the lateral movement of the first end 162about longitudinal axis 195 of the filter housing 132. The ribs 141 arespaced apart from the boss 121 at a lateral distance 131 on each side ofthe boss 121. In some embodiments, the lateral distance 131 isapproximately 1.5 millimeters (mm). The ribs 141 project from the wall193 on the first housing end 127 a projection distance 191. In someembodiments, the projection distance 191 is approximately 2 mm.

The construction and arrangements of the air filter assembly, as shownin the various exemplary embodiments, are illustrative only. Althoughonly a few embodiments have been described in detail in this disclosure,many modifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Someelements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process, logicalalgorithm, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present invention.

What is claimed is:
 1. An internal combustion engine, comprising: anengine block including a cylinder; an air-fuel mixing device configuredto provide an air-fuel mixture to the cylinder; an air filter assemblyconfigured to provide filtered air to the air-fuel mixing device,comprising: a housing comprising a base and a cover, wherein the baseand the cover define an interior volume, wherein the housing comprisesan air intake, a filtered air outlet, and an outlet passage fluidlycoupling the filtered air outlet to a final air outlet; a filter elementpositioned within the interior volume, the filter element divides theinterior volume into a filtered volume and an unfiltered volume; and agap between the filter element and the housing configured to direct airin a first airflow pass before being filtered by the filter element;wherein the filter element is configured to direct filtered air in asecond airflow pass in a substantially opposite direction from the firstairflow pass; and wherein the outlet passage is configured to directfiltered air into a third airflow pass in a substantially same directionas the first airflow pass.
 2. The engine of claim 1, wherein the coveris configured to releasably fasten to the base, and wherein the housingcomprises a first housing end portion and a second housing end portion.3. The engine of claim 2, wherein the base comprises the air intake, thefiltered air outlet, and the outlet passage.
 4. The engine of claim 2,wherein the first housing end portion comprises the air intake and thefiltered air outlet, and wherein the second housing end portioncomprises a debris outlet configured to allow debris and air to exit thehousing.
 5. The engine of claim 2, wherein the gap is configured todirect air in the first airflow pass in a direction from the firsthousing end portion toward the second housing end portion.
 6. The engineof claim 1, wherein the housing further comprises a plurality of ribsformed in the cover and the base to direct air from the air intaketoward a debris outlet formed in the base.
 7. The engine of claim 6,further comprising a trough formed in the base near the debris outlet,wherein the trough narrows from an entrance to an exit and is configuredto direct debris toward the debris outlet.
 8. The engine of claim 6,wherein the plurality of ribs extend more than halfway into the gap. 9.The engine of claim 6, wherein the plurality of ribs in the covercomprise helical ribs and the plurality of ribs in the base comprisehelical ribs.
 10. The engine of claim 6, wherein the plurality of ribsin the cover align with the plurality of ribs in the base to form aplurality of angled air channels within the housing.
 11. The engine ofclaim 10, wherein the first of the plurality of angled air channels isnarrower than a remainder of the plurality of angled air channels;wherein the first of the plurality of angled air channels is positionedproximate the air intake such that air enters the first of the pluralityof angled air channels before entering the remainder of the plurality ofangled air channels.
 12. The engine of claim 1, wherein the air intakecomprises an L-shape having a first portion and a second portion;wherein the first portion is configured to direct incoming air flow tosubstantially complete a first filtering pass within a first angled airchannel before joining with incoming air flow from the second portion.13. The engine of claim 1, wherein the air filter assembly is orientedhorizontally with the engine in a normal operating position.
 14. An airfilter assembly configured to provide filtered air to an engine,comprising: a housing comprising a cover and a base, wherein the coverand the base define an interior volume of the housing; a filter elementpositioned within the interior volume and comprising filter media, thefilter element divides the interior volume into a filtered volume and anunfiltered volume; an air intake formed in the base and configured toallow air to flow into the housing; a debris outlet formed in the baseand configured to allow debris and air to exit the housing; a filteredair outlet formed in the base, wherein the filtered air outlet isfluidly coupled to an air-fuel mixing device to allow filtered air toexit the housing and enter the air-fuel mixing device; a gap between thefilter element and the housing configured to allow air to flow betweenthe filter element and the housing; and a plurality of ribs formed inthe cover and the base configured to direct air to complete at least twocyclonic filtering passes within the gap before being filtered by thefilter element.
 15. The air filter assembly of claim 14, wherein theplurality of ribs extend more than halfway into the gap.
 16. The airfilter assembly of claim 14, wherein the plurality of ribs in the coveralign with the plurality of ribs in the base to form a plurality ofangled air channels within the housing.
 17. The air filter assembly ofclaim 16, wherein one of the plurality of angled air channels isnarrower than a remainder of the plurality of angled air channels;wherein the one of the plurality of angled air channels is positionedproximate the air intake such that incoming air enters the one of theplurality of angled air channels before entering the remainder of theplurality of angled air channels.
 18. The air filter assembly of claim14, further comprising a trough formed in the base near the debrisoutlet, wherein the trough is configured to direct debris toward thedebris outlet.
 19. The air filter assembly of claim 14, wherein airflows into the housing from the air intake based on intake pressurepulses created from reciprocation of a piston.
 20. An internalcombustion engine, comprising: an engine block including a cylinder; anair-fuel mixing device configured to provide an air-fuel mixture to thecylinder; an air filter assembly configured to provide filtered air tothe air-fuel mixing device, comprising: a housing comprising a base anda cover, the cover is configured to releasably fasten to the base, thehousing defining a first housing end portion and a second housing endportion, wherein the base and the cover define an interior volume; afilter element positioned within the interior volume, the filter elementdivides the interior volume into a filtered volume and an unfilteredvolume; an outlet passage formed in the base fluidly coupling a filteredair outlet to a final air outlet, the filtered air outlet in fluidcommunication with the filtered volume of the filter element; an airintake formed in the housing at the first housing end portion andconfigured to allow air to flow into a gap between the filter elementand the housing, wherein the gap is configured to direct air in a firstairflow pass in a direction from the first housing end portion towardthe second housing end portion before being filtered by the filterelement; wherein the filter element is configured to direct filtered airin a second airflow pass in a substantially opposite direction from thefirst airflow pass; and wherein the outlet passage is configured todirect filtered air into a third airflow pass in a substantially samedirection as the first airflow pass.